Objective:
To determine how length of anticoagulation and clinical presentation of venous thromboembolism influence the risk of recurrenceafter anticoagulant treatment is stopped and to identify the shortest length of anticoagulation that reduces the risk of recurrence to its lowest level.

Population:
2925 men or women with a first venous thromboembolism who did not have cancer and received different durations ofanticoagulant treatment.

Main outcome measure:First recurrent venous thromboembolism after stopping anticoagulant treatment during up to 24 months of follow-up.

Results:Recurrence was lower after isolated distal deep vein thrombosis than after proximal deep vein thrombosis (hazard ratio 0.49, 95% confidence interval 0.34 to 0.71), similar after pulmonary embolism and proximal deep vein thrombosis (1.19, 0.87 to 1.63), and lower afterthrombosis provoked by a temporary risk factor than after unprovoked thrombosis (0.55, 0.41 to 0.74). Recurrence was higher if anticoagulation was stopped at 1.0 or 1.5 months compared with at 3 months or later (hazard ratio 1.52, 1.14 to 2.02) and similar if treatment was stopped at 3 months compared with at 6 months or later (1.19, 0.86 to 1.65). High rates of recurrence associated with shorter durations of anticoagulation were confined to the first 6 months after stopping treatment.

Conclusion:
Three months of treatment achieves a similar risk of recurrent venous thromboembolism after stopping anticoagulation to a longer course of treatment. Unprovoked proximal deep vein thrombosis and pulmonary embolism have a high risk of recurrence whenevertreatment is stopped.